1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to a transmitter transmitting at high data rates with such wireless communication systems.
2. Description of Related Art
Communication systems support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, BLUETOOTH™, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
For each wireless communication device to participate in wireless communications, it may include a built-in radio transceiver (i.e., receiver and transmitter) or may be coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). The transmitter may include a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
The transmitter may include a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage can convert raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
The transmitter includes at least one antenna for transmitting the RF signals, which are received by a single antenna, or multiple antennas, of a receiver. When the receiver includes two or more antennas, the receiver will select one of them to receive the incoming RF signals. In this instance, the wireless communication between the transmitter and receiver is a single-output-single-input (SOSI) communication, even if the receiver includes multiple antennas that are used as diversity antennas (i.e., selecting one of them to receive the incoming RF signals). For SISO wireless communications, a transceiver includes one transmitter and one receiver.
Other types of wireless communications include single-input-multiple-output (SIMO), multiple-input-single-output (MISO), and multiple-input-multiple-output (MIMO). In a SIMO wireless communication, a single transmitter processes data into radio frequency signals that are transmitted to a receiver. The receiver includes two or more antennas and two or more receiver paths. Each of the antennas receives the RF signals and provides them to a corresponding receiver path (e.g., LNA, down conversion module, filters, and ADCs). Each of the receiver paths processes the received RF signals to produce digital signals, which are combined and then processed to recapture the transmitted data.
For a multiple-input-single-output (MISO) wireless communication, the transmitter includes two or more transmission paths (e.g., digital to analog converter, filters, up-conversion module, and a power amplifier) that each converts a corresponding portion of baseband signals into RF signals, which are transmitted via corresponding antennas to a receiver. The receiver includes a single receiver path that receives the multiple RF signals from the transmitter. In this instance, the receiver uses beam forming to combine the multiple RF signals into one signal for processing.
For a multiple-input-multiple-output (MIMO) wireless communication, the transmitter and receiver each include multiple paths. In such a communication, the transmitter parallel processes data using a spatial and time encoding function to produce two or more streams of data. The transmitter includes multiple transmission paths to convert each stream of data into multiple RF signals. The receiver receives the multiple RF signals via multiple receiver paths that recapture the streams of data utilizing a spatial and time decoding function. The recaptured streams of data are combined and subsequently processed to recover the original data.
In addition, current wireless local area network standards also need to be considered. With respect to IEEE 802.11a, such communication can operate at 5 GHz frequency bands, which can achieve up to 54 Mbps based on Orthogonal Frequency Division Multiplexing (OFDM). With respect to IEEE 802.11b, such communication can operate at 2.4 GHz, which can achieve up to 11 Mbps based on DSSS-CCK (Direct Sequence Spread Spectrum—Complementary Code Keying). Both types of wireless communication been widely used. In order to achieve the higher data rates at 2.4 GHz, IEEE 802.11g was approved in 2003 by adopting OFDM to achieve 54 Mbps. For coexistence with existing 802.11b system in 2.4 GHz bands, 802.11g was designed to have backward compatibility. Such systems are all SISO systems.
Giving consideration to more reliable and faster data transmission systems, MIMO may be applied in IEEE 802.11n. Among many other techniques considered, Space-Time Block Coding (STBC) is one of popular choices to enhance the transmission coverage. However, due to the unique design of STBC over pairs of transmit antennas, the MIMO may be bulky to utilize STBC MIMO design to enhance the coverage, as well as 5150 design for existing IEEE 802.11a/b/g. In order to have additional data paths, there may be additional costs to including both legacy and STBC implementations. Therefore, there is a need for simpler approaches that allow for backward compatibility and simplicity of design.